Wet spinning of acetic acid solutions of cellulose acetate



May '19, 1964 NET SPINNING J. RUSSELL 3,133,979 OF ACETIC ACID SOLUTIONS OF CELLULOSEZ ACETATE Filed Nov. 16, 1962 United States Patent 3,133,979 WET SPINNING 0F ACETIC ACID SOLUTIONS OF CELLULOSE ACETATE James Russell, New Qity, N.Y., assignor, by mesne assignments, to FMC Corporation, San Jose, Calif., a

corporation of Delaware Filed Nov. 16, 1962, Ser. No. 238,275 12 Claims. (Cl. 264200) This invention relates to a method for the preparation of shaped articles of cellulose acetate. More particularly, it relates to a method for the wet spinning of filaments and fibers from an acetic acid solution of cellulose acetate having an acetyl value of about 30% up to 62.5% determined as acetic acid.

This is a continuation-in-part of applicant's prior c0- pending application Serial No. 129,992, filed August 8, 1961, now abandoned.

The dry spinning of cellulose acetate from a volatile solvent yields a relatively low tenacity yarn. The wet spinning of such a material into a solvent/non-solvent mixture can produce a yarn of improved physical properties. However, preparation of the spinning solution requires that the cellulose acetate be precipitated from the acetylation mixture, washed, dried and then redissolved. It would be desirable if the acetylation mixture itself, commonly termed cellulose acetate acid dope, could be spun directly to produce a yarn of desirable physical properties. Attempts have been reported using spin baths of acetic acid/water mixtures to precipitate cellulose acetate acid dopes but the yarn produced in general was found to have properties which are inferior to those produced by wet spinning cellulose acetate from volatile solvents.

It is a primary object of this invention to provide a method for wet spinning of cellulose acetate acid dope to produce shaped articles of desirable mechanical properties.

It is another object of this invention to provide a method wherein either primary, secondary or a lesser substituted cellulose acetate acid dope can be wet spun to produce filaments of desirable mechanical properties.

These and other objects of the invention are accomplished by a method for preparing shaped articles of cellulose acetate which comprises forming a shaped article from a solution of cellulose acetate in acetic acid and coagulating said article in a bath consisting essentially of from to 65% and preferably from 20 to about 55% by weight of acetic acid, and an aliphatic dihydric alcohol. The cellulose acetate solution or acid dope is usually shaped by extruding it through one or more holes or a slot to form continuous filaments or a film. Since the process is particularly useful for forming filaments having improved tenacity and elongation characteristics, the invention will be particularly described in connection with filaments and fibers.

The accompanying drawing shows an embodiment of the invention including a coagulating bath 2'containing a mixture of acetic acid and aliphatic dihydric alcohol, and spinneret 4 from which an acetic acid solution of cellulose triacetate is extruded. The yarn is drawn from the bath under godet 6 and over driven godet 8 which exerts a primary stretch on the yarn coming from the spinneret 4. The yarn proceeds under godets 10 and 12 in water wash bath 14. A secondary stretch may be imposed between godets 10 and 12 if desired by driving godet 12 at higher speed than godet 10. The yarn then passes over drying rolls 16 and 18 and wound up on roll 20.

The cellulose acetate articles of this invention have a degree of acetylation, specified as percent combined acetic acid, which is preferably above 30%. Secondary cellu- 3,133,979 Patented May 19, 1964 lose acetate generally has an acetyl value of from about 54 to about 56% while primary cellulose acetate has an acetyl value of over 60%.

The spinning solution of cellulose acetate in acetic acid is most conveniently prepared by the acetylation of cellulose with acetic anhydride, in the presence of acetic acid as solvent and of sulfuric acid as catalyst. When the acetylation reaction, in this procedure, is substantially complete, the reaction mixture consists of a solution of cellulose in which or more of the hydroxyl groups are esterified with acetic acid and the majority of the remaining hydroxyl groups are esterified with sulfuric acid; the solution also contains some free sulfuric acid catalyst and some excess acetic anhydride. The conversion of this solution to a solution suitable for spinning requires, first, that a quantity of water be introduced suflicient to react with the residual anhydride, to hydrolyze the sulfate ester present and to provide a small excess. If it is desired to produce a secondary or lesser substituted cellulose acetate, additional water is added to hydrolyze part of the acetyl content of the primary cellulose ester to produce a cellulose acetate having the desired degree of substitution. Following this addition the solution is agitated for a length of time and at a temperature suilicient to reduce the sulfate ester content of the polymer to an acceptably low level. Next there is added, in suitable form for rapid mixing, a neutralizing agent in quantity sufficient to combine with the sulfuric acid acetylation catalyst and to provide a small excess to insure completeness of neutralization. The resulting solution is filtered using procedures well known in the art, and is then ready for spinning. While it is most convenient to prepare the spinning solution of this invention by the method described above, this invention is not limited to solutions prepared by that method but applies to the spinning of any solution containing cellulose acetate dissolved in a solvent of which the major constituent is acetic acid. The concentration of cellulose acetate in such a solution should be, preferably, between 8 and 15%. The degree of polymerization of the polymer may have any value sutiicient to permit the formation of fibers, but for best fiber properties it should be above 350 and, preferably, as high as 450.

The coagulating or spinning bath of this invention contains an amount of acetic acid broadly ranging from about 10% to 65% and preferably ranging from about 20% to about 55% by weight. When spinning the triacetate solutions spin baths containing from about 35 to about 55% acetic acid are preferred, while in the spinning of secondary and lesser substituted acetate solutions spin baths containing from about 10 to about 30% acetic acid are preferred. The acetic acid is mixed with an aliphatic dihydric alcohol, which is generally a liquid or otherwise becomes liquid when mixed with the acetic acid. The aliphatic dihydric alcohols, which are nonsolvent materials for cellulose acetate, include, for example, ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, 2,2-dimethyl-1,3-propanediol; 2,2,3, S-tetramethyl-1,4-butanediol; 2-butene-l,4-diol; 2-hexene- 1,6-diol; 3-octene-l,8-diol; 2,2,5,S-tetramethyl-S-hexene- 1,6-diol; diethylene glycol, triethylene glycol, tetraethyl- 'ene glycol, dipropylene glycol, 4,4-dihydroxy-dibutyl ether; other polyoxyalkylene glycols, such as polyethylene glycol, having average molecular weights up to about 1000. Members of the Carbowax series up to 1000 are representative of useful polyethylene glycols. Mixtures of dihydric alcohol non-solvents may also be employed, together with acetic acid, in the practice of my invention. Also, mixtures consisting of acetic acid, a dihydric alcohol or mixture of dihydric alcohols, and a small amount of another liquid may be employed, provided the presence of the other liquid in question does not modify appreciably the action of the bath or the properties of the product. For example, in the cases in which ethylene glycol or polyoxyethylene glycol of molecular weight 200 to 1000 is employed as the dihydric alcohol constituent, a small amount of water, up to of the bath by weight, has been found to be without appreciable effect.

The production of yarns or of staple fiber according to the known art of wet spinning is a complex process which incorporates a number of individual procedures in sequence. Such procedures include flow modifying means around the newly formed fibers in the coagulating bath, snubbing devices and godet Wheels for the application of both primary and secondary stretch, and mechanical retraction control means. Other common procedures including washing free of solvent, cutting, crimping, drying, collecting to form a package, etc, are used for the purpose of placing the fully formed filaments in a condition suitable for sale to the textile trade. In accordance with the present invention a complete spinning process will be required which will combine procedures enumerated above in such a way as to insure controlled, continuous product having certain desired properties and in a form suitable for commercial use.

In general, the properties of filaments or fibers are determined by the composition and temperature of the spinning solution and of the coagulating bath and also by the combination of procedures and conditions of application thereof which are designed to modify filament properties in the course of their formation.

Because of the number of useful variations in conditions and procedures, and also because of the large number of dihydric alcohols and mixtures thereof which may be employed in practicing my invention, it is not possible to state an optimum spinning temperature or optimum coagulating bath composition within the given range which will be applicable to all bath compositions and to all detailed steps of other spinning variables.

Broadly stated the operable spinning bath temperature ranges from just above the freezing temperature of the acid dope, about C., to about 80 C. and above. It is preferred, however, on the basis of good spinning results and convenience of spinning operation that the spin bath temperature range from about 30 to about 50 C.

The length of travel and the speed of travel of the coagulated filaments in the spinning bath belong to the large group of detailed conditions which are interdependent in their effects, so that it is meaningless to specify them apart from other process conditions.

When cellulose acetate acid dope is extruded through fine orifices into a coagulating bath of a composition as described above, the streams of dope coagulate to form filaments which may be drawn away from the orifices and eventually out of the bath in accordance with the known art of wet spining. We define the term primary stretch factor as the ratio of the linear velocity with which the filaments are withdrawn from the coagulating bath to the calculated average linear velocity of extrusion of the acid dope through the spinning orifices. It is observed in spinning into the coagulating baths of this invention that the primary stretch factor may have a wide range of values, up to 10 or more. In contrast, when cellulose acetate acid dope is coagulated in a bath consisting of acetic acid and water as major constituents the primary stretch factor must have a value of 1.0 or below if the properties of the final product are not to be adversely affected. One practical advantage of this major difierence in the coagulation process in my invention as compared to that which takes place in aqueous acetic acid baths is that filaments of very fine denier may be spun without the use of jet holes of inconveniently small size.

In the art of wet spinning it is a common practice to increase the tenacity of the product by the application of stretch beyond the coagulating bath, between a godet, or other snubbing device, at the exit from the bath and a second godget. The ratio of the output to input linear velocities in such a stretching operation will be denoted by the term secondary strength factor. Finally, it is possible in some cases to modify the properties of the final product desir'ably by permitting a controlled degree of retraction or relaxation of the filaments subsequent to stretching. Such a relaxation operation may also be described mathematically by a stretch factor defined as the ration of output to input speeds, which in this case will be less than unity. The total stretch factor applied to a yarn will be the product of the stretch factors for the individual stages of its preparation.

It is possible to modify the effects of primary stretch in the coagulating bath by introducing a yarn guide or other snubbing device intermediate between the spinning orifices and the point of exit of the yarn from the bath. The effect of such a snubbing device is to increase the tension acting upon the travelling filaments in the region between the snubbing device and the device used to withdraw the filaments from the coagulating bath. The effect of this increase of tension is similar to the effect of secondary stretching beyond the coagulating bath proper; it tends to produce molecular orientation and to increase the final strength of the filaments while reducing their extensibility. It is to be understood that these various known procedures, as described in the foregoing paragraphs, either singly or in combination, may be used in the practice of spinning according to my invention.

It is an advantage of my invention that the constituents of the coagulating bath are relatively non-volatile so that secondary stretching or relaxation operations may be conducted upon filaments after their withdrawal from the coagulating bath without the filaments changing in composition at too rapid a rate because of volatilization of the swelling liquid present in such filaments before washing. Other characteristics of these baths which are advantageous are (1) their constituents are miscible with water and may be removed from the filaments by washing with water (2) they possess moderately high viscosity, which facilitates control of bath turbulence which might otherwise be destructive of the filaments in the early stages of their formation.

Various combinations of primary stretch, secondary stretch and relaxation may produce yarns of widely varying properties from a given spinning dope and detailed set of coagulating bath conditions. These yarns will be characterized by varying tenacity and extensibility, as measured by standard methods in an atmosphere of controlled temperature and humidity.

It is sometimes useful to compare yarns in terms of a single number characterizing their mechanical quality. For this purpose I use the breaking stress, or the stress in the yarn at the point of breaking on a testing machine, expressed in grams per denier and referred to the denier at the instant of rupture. The breaking stress (denoted T is related to the tenacity (T) as measured in the same experiment by the equation E T T 1 where E is the extensibility, in percent of initial length, also measured in the same experiment. I have found that filaments spun according to my invention possess excellent mechanical properties expressed in terms of breaking stress, tenacity and elongation, as will be illustrated in the description of the following examples.

Example I An acetylation mixture was prepared by first charging 2130 grams of cellulose pulp into a reaction vessel containing 1920 mls. of acetic acid and stirring for one hour at 30 C. A mixture of 12,400 mls. of acetic acid and 10.9 mls. of sulfuric acid was then added and stirring continued for 45 minutes while the temperature of the vessel was reduced to and then maintained at 16 C. Next, 1292 mls. of acetic anhydride and a mixture of 192 mls. of acetic acid and 5.5 mls. of sulfuric acid were added in succession and stirring continued for 30 minutes at 16 C. Next 4060 mls. of precooled acetic anhydride was charged to the vessel. After 5 minutes delay the temperature of the vessel was raised to 30 C. over a 30 minute period, during which a mixture of 763 mls. of acetic acid and 60 mls. of sulfuric acid was added. Stirring was then continued at 30 C. until the reaction mixture became homogeneous and clear and for sufiicient time thereafter to reduce its viscosity to 1000 poise. Hydrolysis of excess acetic anhydride and of sulfate ester groups on the cellulose was then brought about by metering in a mixture of 1720 mls. of acetic acid and 248 mls. of water at the rate of 100 mls. per minute; the temperature was raised to 45 C. during this addition and maintained there for an additional minutes after its completion. Thereafter, the sulfuric acid catalyst was neutralized by the addition of 260 gms. of sodium acetate dissolved in 1920 mls. of acetic acid, in 5 increments at 1 minute intervals.

The weight composition of the neutralized cellulose triacetate dope was as follows:

Percent Cellulose triacetate 12.54

Water 0.36 Acetic Acid 85.7

Sulfate .49

Sodium acetate .92

After suitable filtration this cellulose triacetate acid dope was extruded through a spinneret containing 40 holes or 3 mils diameter, into a mixture of equal parts by weight of ethylene glycol and glacial acetic acid maintained at a temperature of 35 C. The dope was pumped through the jet at 0.6 ml. per min. and the filaments withdrawn from the bath by means of a godet, at a speed of 13 meters per minute, washed, and dried without tension. A yarn having an average filament denier of 1.5, a conditioned tenacity of 2.0 grams per denier, an elongation at break of 20% and a breaking stress of 2.4 gm./ den. was obtained.

A spinning experiment was conducted identical to the above except that the coagulating bath consisted of 30% by weight of acetic acid and 70% of isopropanol and was maintained at a temperature of 55 C. Proportions of acetic acid in the bath over 40% produced cemented yarns. The best yarn which could be obtained at an average filament denier of 1.5 had conditioned tenacity of 1.8 grams per denier, an elongation at break of 12% and a breaking stress of 2.02 gm./den. When the bath temperature was lowered to 35 C. a still poorer yarn resulted.

in further comparison with the above, the best yarns which have been spun into a spin bath consisting of acetic acid and water were obtained at an acetic acid concentration of 20% and a temperature of C. Using the same cellulose triacetate acid dope and a spinneret having holes of 1.5 mil diameter (in order to obtain the desired 1.5 denier filaments) a yarn was obtained which, after a secondary stretch of from 50 to 60% had a conditioned tenacity of 2.0 grams per denier, an elongation at break of 13% and a breaking stress of 2.26 gm./den.

Example 11 Cellulose triacetate acid dope as described for Example I was extruded vertically upward at a rate of 0.6 ml. per min. through a spinneret, containing 40 holes each 3 mils in diameter, immersed in a bath containing 55% by weight of a polyethylene glycol having an average molecular weight of about 400 (Carbowax 400) and 45% by weight of glacial acetic acid at a bath temperature of 40 C. The emerging fiiaments were drawn over a guide 9 /2 inches from the face of the jet, and over two 6 godet wheels rotating in a bath of water at 50 C. between which a stretch of 50% was applied. After the stretching stage the filaments were run through a second water wash bath at room temperature, collected at a speed of 13 meters/ minute, and dried.

The resulting yarn had an average filament denier of 1.4, a conditioned tensile strength of 2.44 gm./den., an elongation at break of 10.9%, and a breaking stress of 2.7 gm./den.

Example III Cellulose triacetate acid dope as described for Exampic I was extruded vertically upward into a bath containing 55% by weight of a polyethylene glycol having an average molecular weight of about 200 (Carbowax 200) and 45% by weight of glacial acetic acid, in the manner described in Example II. The emerging filaments were passed over two guides, the first being 44 inches above the jet and the second 23 inches below the first and in the same horizontal plane as a first godet. The yarn then passed from the first godet through a water bath to a second godet rotating at 28% higher surface speed, and was then collected and dried. The final yarn speed was 13 meters per minute.

The resulting yarn had a filament denier of 1.5, a tensile strength of 2.10 gm./den., an elongation at break of 16% and a breaking stress of 2.4 gm./ den.

Example IV Cellulose triacetate acid dope was prepared, neutralized and filtered as in Example I. It was then extruded at 0.6 ml. per minute through a spinneret as described in Example II into a coagulating bath composed of 40% acetic acid and 60% propylene glycol, maintained at 30 C. The yarn was withdrawn from the bath at 13 meters per minute, passed through a water wash bath to a second godet also rotating at a speed of 13 meters per minute, collected, and dried in a relaxed state. No snubbing guide was used in the bath. The yarn, of 1.5 denier per filament, possessed a tenacity of 1.7 gm./den., an elongation of 19%, and a breaking stress of 2.03 gm./den.

Example V Cellulose triacetate acid dope prepared, neutralized and filtered as in Example I was extruded at 0.6 m1./min. through a spinneret as described in Example II into a bath consisting of 35% acetic acid and 65% ethylene glycol maintained at 50 C. The yarn passed vertically upward from the spinneret through an eight-inch depth of bath, thence to and over a guide supported thirty inches above the bath surface, downward to a second guide situated eight inches below the first, and then horizontally to a first godet rotating with a surface speed of 8.67 m./min. From the first godet it passed to a second godet rotating at 13 m./min. surface speed, undergoing a 50% stretch between the godets, and was then washed and dried relaxed. The resulting yarn, of 1.5 den./fil., had a tenacity of 2.20 gm./den., an elongation of 14.1% and a breaking stress of 2.51 gm./den.

Example VI Dope was prepared as in Example I and spun under conditions as described in Example V except that the second snubbing guide located just before the first godet was omitted, the yarn passing downward at an angle to the vertical direction from the first snubbing guide directly to the first godet.

(a) The yarn then passed from godet 1 to godet 2 both operated at 13 meters/min. surface speed, and was then washed and dried in a relaxed state. The yarn, of 1.5 den./fil., was tested and found to have a tenacity of 1.73 gm./den., an elongation of 25.1%, and a breaking stress of 2.16 gm./den.

(b) Godet 1 was operated at 8.67 m./min. and godet 2 at 13 m./min. The yarn passed from godet 1 to godet 2, being stretched 50% between them, and was then washed and dried relaxed. The yarn, of 1.5 den./fil., had a tenacity of 2.33 gm./den., an elongation of 12.6% and a breaking stress of 2.62 gar/den. The improvement of tenacity and of breaking stress achieved in (b) as compared with (a) is to be understood as the result of increased chain molecule orientation in the fiber axis direction resulting from the stretch between godets.

Example VII A secondary cellulose acetate acid dope was prepared in accordance with the procedure for preparing the acid dope of Example I except that additional water was added during the hydrolysis step to hydrolyze part of the acetyl content to produce a cellulose ester having a degree of substitution of about 2.4 (corresponding to an acetyl Value of 55.4% determined as acetic acid). After filtration the resulting solution was spun through a 40 hole jet vertically into a tube containing a spin bath of 80% by weight of a polyethylene glycol having an average molecular weight of about 600 (Carbowax 600) and acetic acid. The yarn was withdrawn from the bath by a godet at a linear speed of 28 feet per minute and led through two wash baths of water. The temperature of the spin bath was 40 C. The temperatures of the wash baths were maintained at C. and 90 C. respectively. The yarn was dried in a relaxed state after washing. It had a denier of 58.5, a tenacity of 2.04 grams per denier and an extensibility of 14.6%

It is obvious from the above examples that the process of this invention produces yarn of surprisingly superior properties.

While this invention has been described in particular with regard to filaments and fibers, other shaped articles of cellulose triacetate such as films, foils, sheets, ribbons, etc., having improved strength and elongation characteristics may be manufactured according to the general procedure described herein.

Various changes and modifications may be made in practicing this invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.

I claim:

1. A method of preparing shaped articles of cellulose acetate which comprises forming a shaped article from a solution of cellulose acetate having an acetyl value of from about 30% up to 62.5% in a major proportion of acetic acid, and coagulating said shaped article in a bath consisting essentially of from about 10 to about 65% by weight of acetic acid and an aliphatic dihydric alcohol.

2. The method of claim 1 wherein said shaped article is a filament and said cellulose acetate is present in the solution in an amount ranging from 8 to 15% by weight.

3. A method of preparing cellulose acetate filaments and fibers which comprises spinning a catalyst neutralized, cellulose acetate acid dope containing from about 8 to about 15% by weight of cellulose acetate having an acetyl value of from about 30 up to 62.5% into a coagulating bath consisting essentially of from about 10 to about 65 by weight of acetic acid and an aliphatic dihydric alcohol.

4. A method of preparing cellulose acetate filaments and fibers which comprises spinning a catalyst neutralized, cellulose acetate acid dope containing from about 8 to about 15% cellulose acetate having an acetyl content of from about 54 to about 56% into a coagulating bath consisting essentially of from about 10 to about 30% by weight of acetic acid and an aliphatic di'nydric alcohol.

5. The method of claim 4 wherein the aliphatic dihydric alcohol is a polyoxyalkylene glycol having a molecular weight ranging from about 200 to about 1000.

6. A method of preparing cellulose triacetate filaments and fibers which comprises spinning a catalyst neutralized, cellulose triacetate acid dope containing from about 8 to about 15 by weight of cellulose triacetate into a coagulating bath consisting essentially of from about 35 to 55% by weight of acetic acid and an aliphatic dihydric alcohol.

7. The method of claim 6 wherein the aliphatic dihydric alcohol is ethylene glycol.

8. The method of claim 6 wherein the aliphatic dihydric alcohol is a polyoxyalkylene glycol having a molecular weight ranging from about 200 to about 1000.

9. The method of claim 6 wherein the filaments are subjected to a primary stretch at a stretch factor ranging up to about 11.

10. The method of claim 6 wherein the filaments are subjected to a secondary stretch procedure.

11. The method of claim 4 wherein the filaments are subjected to a primary stretch.

12. The method of claim 4 wherein the filaments are subjected to a secondary stretch.

Dreyfus Sept. 22, 1936 Groombridge Oct. 10, 1961 

1. A METHOD OF PREPARING SHAPED ARTICLES OF CELLULOSE ACETATE WHICH COMPRISES FORMING A SHAPED ARTICLE FROM A SOLUTION OF CELLULOSE ACETATE HAVING AN ACETYLE VALUE OF FROM ABUT 30% UP TO 62.5% IN A MAJOR PROPORTION OF ACETIC ACID, AND COAGULATING SAID SHAPED ARTICLE IN A BATH CONSISTING ESSENTIALLY OF FROM ABOUT 10 TO ABOUT 65% BY WEIGHT OF ACETIC ACID AND AN ALIPHATIC DIHYDRIC ALCOHOL. 